1. Field of the Invention
The present invention relates to compounds, solid polymer electrolyte membranes, electrolyte membrane-electrode assemblies, and solid polymer fuel cells.
2. Description of the Related Art
Perfluoro-based proton conductive polymers, such as Nafion (DuPont) and non-perfluoro-based proton conductive polymers not containing fluorine, have been used as solid polymer electrolyte membranes in fuel cells.
Nafion is a copolymer of perfluorovinyl ether containing a sulfonic acid group and tetrafluoroethylene. It forms an electrolyte membrane having a high proton conductivity.
However, Nafion has a problem in that when it is employed in a direct fuel cell that uses a liquid fuel, such as methanol, the fuel permeability (crossover) is significantly large. Therefore, the energy efficiency is insufficient.
With regard to a solid polymer electrolyte membrane formed of a non-perfluoro-based proton conductive polymer not containing fluorine, a copolymer of a phenylmaleimide derivative having high mechanical strength and a methacrylic acid monomer containing an ion-exchange group has been suggested (Kobunshi Gakkai Yokosyu (Polymer Preprints, Japan, Japanese Ed.) 1999, 48(10), 2393).
However, there is a problem in that the membrane formed of the copolymer of a high mechanical strength phenylmaleimide and a methacrylic acid monomer containing an ion-exchange group cannot readily achieve favorable proton conductivity.